CRM principles start during your first lesson - e.g. we should all understanding during lesson one how to transfer control. The cockpit of any plane is not the place for smart-ass comments from the PIC, SIC, an instructor or a passenger. Nothing wrong with any pilot questioning the actions of another pilot, IMO, but you have to do it in the correct manner. And isn't that one of the things that CRM (or just getting along with other people) is all about?